WO2001011252A1 - Rolling bearing - Google Patents

Abstract

A rolling bearing characterized in that at least the fixed side bearing ring thereof has a lower bainite structure formed by isothermal transformation treatment, a hardness of a HRC of 54 to 64, an amount of retained austenite of 5 % or less, and an area percentage of carbide particles having a length of 0.8 νm or more relative to the total secondary eutectoid carbide area of 20 % or less. The rolling bearing is reduced in the occurrence of white layers.

Description

 Specification

 Rolling bearing

 Technical field

 The present invention relates to a rolling bearing. Background art

 S U J2, a kind of bearing steel, is often used as a material for the bearing ring and rolling elements of rolling bearing parts. For large rolling bearings, SUJ3 and SUJ5 with improved hardenability are used.

 In order to prolong the life of rolling bearings, it is necessary to suppress wear of the raceway surface and surface peeling of the raceway surface, which is called pitching. For this reason, the balance between hardness and toughness is adjusted by subjecting the bearing steel to quenching and tempering to change the structure to a tempered martensitic structure.

 As another method for extending the life, a compressive residual stress is applied to the raceway surface by shot peening. A technique for further utilizing the shot peening process is disclosed in, for example, Japanese Patent Application Laid-Open No. 5-19569. According to this, paying attention to untransformed residual austenite that remains during quenching, the surface part is transformed into martensite by shot-binning to secure hardness, and the inside is left with the austenite as it is to improve ductility. Secured.

 However, in recent years, operating conditions have become severe for bearings for auxiliary parts of motor vehicle engines, and early peeling phenomena, which are difficult to prevent with conventional methods, have become apparent. This early peeling phenomenon is a phenomenon in which the raceway surface peels off in an extremely short time due to a structural change called a white layer, and high shear stress is locally applied to the raceway surface by high vibration and high impact load. It is a phenomenon that occurs.

 In order to suppress the occurrence of such a white layer, it has been proposed to increase the viscosity of a base oil used for lubrication, but there is a problem that the lubrication method is limited.

It is also proposed that the material structure be a stable structure that does not easily cause local deformation. For example, retained austenite decomposes and promotes the formation of white layers. Therefore, it has been proposed to reduce it by sub-zero processing or the like. However, even in this case, generation of a white layer cannot be effectively suppressed.

 In view of the above conventional problems, an object of the present invention is to provide a rolling bearing that can effectively suppress the generation of a white layer. Disclosure of the invention

 In order to achieve the above object, a rolling bearing according to the present invention is characterized in that, in a rolling bearing in which a bearing ring and a rolling element are made of steel, at least a structure of a fixed-side bearing ring has a lower bainite structure by a constant temperature transformation, and HRC = 54 to 64, residual austenite amount is 5% or less, and the area ratio of carbide with a length of 0.8 m or more to the total secondary carbide area is 20% or less. It is assumed that.

 In the rolling bearing having the above configuration, at least the fixed-side bearing ring has a lower bainite structure formed by isothermal transformation. Thereby, the amount of retained austenite is reduced, and the uniformly finely dispersed carbide disperses the acting stress, so that the generation of a white layer can be effectively suppressed. Therefore, the rolling bearing can be stably used for a long period of time even under high vibration and high impact stress conditions.

 That is, the inventor of the present invention causes the formation of a white layer by forming a lower bainite structure in which carbides are more uniformly and finely distributed as compared with a conventional tempered martensite structure by normal quenching and tempering. They found that high shear stress could be effectively dispersed. In addition, the inventors have found that the amount of retained austenite can be reduced by obtaining the lower bainite structure by isothermal transformation. The reason why the present invention has been completed based on such knowledge is that the hardness is set to HRC = 54 to 64 because wear and deformation are apt to occur when the hardness is less than 54, and when the hardness is more than 64. This is because the toughness deteriorates and peeling easily occurs. The amount of residual austenite is set to 5% or less in order to prevent decomposition during rolling as described above and not to promote the formation of a white layer.

The reason why the area ratio of the secondary carbide of 0.8 or more is set to 20% or less is that if it exceeds 20%, the effect of dispersing the acting stress becomes small. The steel used for the bearing is preferably SUJ2. In this case, the mechanical properties can be more effectively improved by the isothermal transformation treatment, and an excellent function of preventing white layer formation can be exhibited. Therefore, it is possible to provide a bearing having a more suitable long life under high vibration and high impact stress conditions. BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, the best mode for carrying out the present invention will be described. However, the present invention is not limited to this.

 [Example 1]

 In Example 1, a workpiece manufactured using SUJ 2 was subjected to austenitizing treatment at 840 for 40 minutes, and then subjected to constant temperature transformation treatment at 230 for 1 hour to obtain a fixed bearing ring of the bearing. I got

 [Example 2]

 In Example 2, a process was performed under the same conditions as in Example 1 except that the holding time of the isothermal transformation was changed to 4 hours, to obtain a bearing-side bearing ring.

 [Example 3]

 In Example 3, a work manufactured using SUJ2 was subjected to austenitizing treatment at 840 for 40 minutes. Thereafter, the holding temperature of the isothermal transformation was set at 260, and the holding time was set at 1 hour to obtain a bearing ring on the fixed side of the bearing.

 [Example 4]

 In Example 4, a process was performed under the same conditions as in Example 3 except that the holding time of the isothermal transformation was changed to 4 hours to obtain a bearing-side fixed bearing ring.

 [Example 5]

 As Example 5, a workpiece manufactured using SUJ2 was subjected to austenitizing treatment at 840 for 40 minutes. Then, the holding temperature of the isothermal transformation was set at 290 ° C, and the holding time was set at 1 hour, to obtain a bearing-side fixed bearing ring.

 [Example 6]

In Example 6, a process was performed under the same conditions as in Example 5 except that the holding time of the isothermal transformation was changed to 4 hours to obtain a bearing-side fixed bearing ring. The isothermal transformation treatments in Examples 1 to 6 were performed by immersing in a salt bath heated and maintained at the transformation treatment temperature.

 Table 1 shows the results of measuring the hardness and the amount of retained austenite in Examples 1 to 6 subjected to the above-mentioned isothermal transformation.

 【table 1】

 By performing the above isothermal transformation, it was confirmed that the material structures of Examples 1 to 6 were a lower bainite structure in which secondary carbides were finely dispersed. As is clear from Table 1, it can be seen that the amount of retained austenite in Examples 1 to 6 is reduced to less than 5%. In addition, the hardness after the isothermal transformation treatment was able to be in the range of HRC-54 to 64 required for rolling bearings from the viewpoint of wear resistance. Further, in all of Examples 1 to 6, the area ratio of carbides of 0.8 m or more to the total secondary carbide area was 20% or less.

 Next, the following test piece 1 and test piece 2 were subjected to a tensile test and an impact test to compare mechanical properties (see Table 2).

 Test piece 1 was prepared by subjecting a tensile test piece and an impact test piece manufactured using SU J2 to an austenitizing treatment at 840 for 40 minutes. The treated product is subjected to isothermal transformation treatment, the hardness is adjusted to HRC = 59, the amount of retained austenite is 5% or less, and the area ratio of carbides of 0.8 m or more to the total secondary carbide area is 20%. It is as follows.

Specimen 2 was adjusted to the same hardness (HRC = 59) by using the conventional method of normal quenching and tempering treatment of the tensile test piece and the impact test piece manufactured using SU J2. What,

 [Table 2]

 As is evident from Table 2, Specimen 1 is superior to Specimen 2 in mechanical properties such as elongation, drawing, and impact value. That is, it is understood that the mechanical properties of SUJ 2 are improved by the above isothermal transformation treatment.

 [Example 7]

 As Example 7, a work made of SU J2 was subjected to an austenitizing treatment at 840 ° C. for 40 minutes. The treated product is subjected to isothermal transformation to a hardness of HR C = 58.9, a residual austenite content of 0.5%, and a carbon area ratio of at least 0.8 im to the total secondary carbide area of 15% or more. The adjusted fixed race was obtained.

 [Comparative example]

 As a comparative example, a conventional quenching and tempering treatment was performed on a work made of SUJ2, the hardness was HRC = 62.6, the amount of retained austenite was 11.6%, and the area of carbides with a length of 0.8 m or more with respect to the total secondary carbide area A 25% fixed bearing ring was obtained. Rolling bearings were manufactured by combining the rolling element made of SU J 2 and the rotating raceway ring, which had been subjected to the conventional quenching and tempering treatment, in Example 7 and Comparative Example, and the white layer was peeled off using a vibration endurance tester. The life was evaluated. The results are shown in Table 3.

 [Table 3]

As is clear from Table 3, the rolling bearing using the comparative example has a service life of 48 to 102 hours before the white layer peels off, whereas the rolling bearing using the embodiment 7 Was confirmed to have a peeling life of more than 1000 hours. Therefore, it can be seen that SUJ 2 is a material that can provide the required hardness, excellent mechanical properties, and a function of preventing white layer formation by isothermal transformation.

 From the above results, it was found that the life of the rolling bearing was improved by at least changing the structure of the fixed-side bearing ring to the lower bainite structure obtained by isothermal transformation, setting the hardness to HRC = 54 to 64, and reducing the residual austenite amount to 5% or less. It was confirmed that this could be achieved by setting the area ratio of carbide with a length of 0.8 or more to the total secondary carbide area to 20% or less.

 The above-mentioned isothermal transformation treatment was applied to the rolling elements and the rotating raceway as well, and the hardness was HR C = 54 to 64, the amount of retained austenite was 5% or less, and 0.8 / m or more with respect to the total secondary carbide area. The area ratio of the carbide having a length may be set to 20% or less. In addition, the material is not limited to SU J2 only.The hardness is HRC = 54 to 64, the amount of retained austenite is 5% or less, and the total secondary carbide area is applied by applying the above isothermal transformation process. Various steels can be used as long as the area ratio of carbides having a length of 0.8 m or more can be reduced to 20% or less.

Claims

Billing 1) For rolling bearings in which races and rolling elements are made of steel,  At least the structure of the bearing ring on the fixed side is a lower bainite structure by isothermal transformation, the hardness is HRC = 54 to 64, the amount of retained austenite is 5% or less, and the length is 0.8 or more with respect to the total secondary carbide area. A rolling bearing characterized in that the area ratio of carbides is 20% or less.  2. The rolling bearing according to claim 1, wherein the steel is SU J2.